Manufacture of antimony oxides



Oct. 7, 1941. A, R BOZARTH 2,258,441

MANUFACTURE 0F ANTIMONY OXIDES Filed Deo. 27, 1959 RR-EO-wm INVENTOR.

` ATTORNEY.

Patented Oct. 7, 1941 MANUFACTURE 0F ANTIMONY OXIDES Abe R. Bozarth, Cleveland, Ohio, assigner to The Iiiarshaw Chemical Company, Elyria, Ohio, a

corporation of Ohio Application December 27, 1939, Serial No. 311,143

9 Claims.

i This invention relates to the production of antimony compounds of high purity and more particularlyr to the 4conversion of an impure grade of SbzOa, that is, one which contains impurities such as sulfur, selenium and lead, and is not in proper physical state for pigment use, to alpuried grade in finely divided state and white enough for pigment and ceramic purposes.

It has been common practice to produce pigment grade antimony oxide (SbzOs) by oxidizing pure antimony metal. This method, although productive of Van excellent product, is expensive and, therefore, a simple, 'effective and relatively'inexpensive process of producing this grade antimony oxide is needed.

I have now discovered that antimony compounds of high purity canbe produced from impure antimony values very cheaply and very simply` by effecting the separation of the antimony values from the volatilizable and the non-volatilizable impurities in separate operations, the

' volatilizable impurities being removed byvolatilization while the antimony is in the form of the tetroxide and the non-volatilizable impurities being removed by volatilizing the antimony in the forni of the trioXide. The latter of these operations is, of course, old,per se. Antimony tetroxide, in nely divided form, that is, in pulverulent orgranular form, can be heated well above the melting point of antimony trioxide l and remain in nely divided form. For this reason, impurities which cannot be volatilized outV of antimony trioxide can easily be removed from antimony tetroxide as gases or vapors. So far vas I am aware, no one prior to my invention has-appreciated the advantages to be derived from these properties of antimony tetroxide as set forth and claimed herein. Indeed. I am not aware that the Iproperties themselves have been fully understood heretofore.

, Accordingly, my invention contemplates the novel process as broadly statedforegoing and as stated in the various claims appended hereto.

Q In the drawing,the iigure is a flow diagram ofy the preferred embodiment of the invention.

First step- In the preferred practice of the invention, I iirst heat the starting material, which may be an impure antimony oxide or sulfide, such as an ore or lpreviously processed impure material -containing non-volatilizable impurities. This material is heated in an oxidizing atmosphere, preferably not departing more than necessary from neutral, under temperature conditions such as to volatilize the antimony trioxide, and the vapors are then condensed.

' ties of impurities.

This step results in the production of SbzOa containing mainly selenium, SOa and lead as impurities. If, as a starting material, I use anti- Inony values which do not contain any nonvolatilizable impurities, this rst step Vmay be omitted. The kiln temperature may vary from 650 C. to 1000 C., but is preferably kept between 700 C. and 800 C., most desirably approximately 800 C.

Second step- I thenV heat the impure SbzOs in an oxidizing atmosphere at a temperature below the melting point of SbzOa'thatY is, below 65OUC., preferably in the range 500 C. to 600 C., and most desirably at` approximately 550 C. Under these conditions, the SbzOa is oxidized, With-out melting, to Sb204 which remains in the form of a fluffy powder; `The temperature should not belallowed to go above the melting point of until oxidation to Sb204 is complete. After oxidation `is complete, the vtemperature may be raised to any desired point short of-the decomposition temperature of SbzOi, which is about 1000 C.-v Inasmuch as-Sb204 has an appreciablevapor pressure and local overheating is possible, it is not desirable to approach'too closely to its decomposition temperature even after oxidation is complete. I prefer to oxidize between V500 C. and 600 C.` and then raise the temperature to a point not exceeding 900. C. preferably between '700 C. and 800 C. The oxidation may occupy from 1 to 2 hours, and I may then heat at the higher temperature for from 1 -to 3 hours, preferably from 2 to 3 hours, in order to reduce as far as possible the quanti- I am not certain as to the state in which the sulfur, selenium, lead, e'tc. are present in the SbzOa nor in what manner they are eliminated, but I believe that they are present in SbzOa in some state of solid solution or chemical combination and that under the conditions above de-l scribed, they are volatilized andV eliminated as gaseous oxides in the case of sulfur and selenium, and as a basic sulfate in the case of lead.

While I prefer to carry out this second step in the manner indicated above, it is obvious that the advantages of the invention may be realized in some degree by operating at a single temperature instead of at two temperatures. Thus, vby

the treatment below the melting point of SbzOa,4

the impurities are removed to a considerable extent and extended heating at such temperature would remove more. On the other hand, heating above the melting point of SbzOa would remove impurities to a large extent but would result in loss of antimony.

Third step-The substantially pure Sb2O4 is. then mixed with carbon or other suitable reducing agent under conditions to reduce the Sb204 to SbzOe. This result is best obtained by mixing just the proper amount of substantially pure, finely divided carbon such as lamp black, ground Wood charcoaly or the like and heating at a ternperature suiiicient to volatilize the SbzOa as it is formed. The retort in which this operation is carried out is placed under suction so as to withdraw SbzOa as formed and this product` is cooled so as to precipitate a very 'nely divided material.

Alternatively, I may conduct the iirstvv step under suiciently highly oxidizing conditions to form the tetroxide from, for example, the suliide ore, prolonging the heating to remove the volatilizable impurities such as sulfur, selenium and lead, thereby producing a product containing only non-volatilizable impurities, and then reducev the tetroxidel to the trioxide under conditions to fume off the latter as formed, leaving the non-volatilizable impurities behind.

Obviously, if the third step is omitted', the process is well adapted to the production of highly pure antimony tetroxide.

E .Tample Sti-buite was heated' in a rotary retort at a temperature held between: 800 C. and 1000 C. and.' in an oxidizing atmosphere until the antimony content had been fumed off in the form oi SbzOa.. This SbzOs and other gases produced therewith were passed into a cooler and bag iilter where the SbzOa and some' impurities were collected. Uncondensed impurities, mainly SO2, Were'removed. The SbzOs, now free of nonvolatilizable impurities was roasted at a temperature maintained between 500 C. and 600 C. i-nan: oxidizing atmosphere for a period of 2 hours until the SbzOa was converted to Sb204. The temperature. was ,thenraised to and maintained; between r150" C. and 850 C. for a period of 3-v hours. The substantially pure Sb204 was then mixed with Wood' charcoal in theoretical quantity required to reduce theA Sb2O4 to SbzOs and heated to a temperature of 800 C. to 1000 C. whereby the Sb204 was reduced' to SbzOs and iumed 01T as formed. The SbzOa was condensed and4 recovered as a pure white iinely divided product containing less than 0.1% sulfur, less than 0.01% selenium, and less than 0.1% lead.

Having thus described' my invention, what I claim is:

1. A method of'producing pure antimony compounds comprising removing volatilizable and non-volatilizable impurities from antimony values by separate operations, volatilizable impurities including one or more elements of the class consistingl of sulfur, selenium and lead, being removed by volatilizationwhile the antimony is, in the form of the tetroxide, and non-volatilizable impurities. being removed by volatilizing the antimony in the form of the trioxide, whereby such impurities are left behind, thevolatilized antimony trioxide being condensed at a place spaced from such non-volatilizable impurities.

2. In a process for producing a pure antimony trioxide, the steps of heating antimony tetroxide, containing one or more impurities of the class consisting of sulfur, selenium and lead, under oxidizing conditions to volatilize Such impurity or impurities, removing the volatilized impurities from the antimony tetroxide and then reducing the so purified tetroxide to the trioxide.

3. In a process for producing a pure antimony trioxide, the steps oi heating pulverulent antimony tetroxide, containing one or more impurities of the class consisting of sulfur, selenium and lead, under oxidizing conditions to volatilize such impurity or impurities and then reducing the so purified tetroxide to the trioxide.

4. In a process for producing a pure antimony trioxide, the stepsV of heating antimony tetroxide, containing one or more impurities of the class consisting of sulfur, selenium and lead, under oxidizing conditions and above the melting point ofA SbaOs to volatilize such impurity or impurities and then reducing the so puriiied tetroxide to the trioxide.

5. In a process for producing a pure antimony trioxide, the steps of heating pulverulent antimony tetroxide, containing one or more impurities of the class consisting of sulfur, selenium and lead, under oxidizing conditions and above the melting point of SbzOs to volatilize such impurity or impurities and then reducing the so puried tetroxide to the trioxide.

6. A process of. purifying antimony trioxide, containing one or more impurities of the class consisting of sulfur, selenium and lead, comprising the steps of converting the same to the tetroxide by heating under oxidizing conditions below the melting point of the trioxide, then elevating the temperature to a point above the melting point of the trioxide but below the decomposition temperature of the tetroxide maintaining such elevated temperature while removing the volatilized impurities until the desired purity is attained and then reducing the substantially pure tetroxide to the trioxide.

7. A method of producing substantially pure. antimony tetroxide comprising oxidizing antimony trioxide to the tetroxide by heating under oxidizing conditions below the melting point of the trioxide until the oxidation is substantially complete, thereby forming a pulverulent,r finely divided tetroxide and then heating the resulting tetroxide under oxidizing conditions at a temperature above the melting point of the trioxide and below the decomposition temperature of the tetroxide whereby to remove impurities by volatilization.

8. In purification of antimony Values, that improvement which comprises removing volatilizable impurities by heating antimony tetroxide containing such impurities under oxidizing conditions at a temperature above 650 C. and below 1000 C.

9. In purification of antimony values, that improvement which comprises the steps of converting finely divided antimony trioxide containing volatilizable impurities into nely divided antimony tetroxide by heating in an oxidizing atmosphere below 650 C. and then removing volatilizable impurities by heating in an oxidizing atmosphere at a temperature above 650 C. andbelow 1000 C.

ABE R. BOZARTH, 

